Viability of aromatic all-pnictogen anions (original) (raw)
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Journal of Physical Chemistry A, 2002
The electronic structure and chemical bonding of the pentapnictogen cluster anions, Pn 5-(Pn) P, As, Sb, and Bi), were investigated using both photoelectron spectroscopy and ab initio calculations. Well-resolved photoelectron spectra were obtained for the anions at several photon energies and were analyzed according to the theoretical calculations. The ground state of all the Pn 5species was found to be the aromatic cyclic D 5h structure with a C 2V low-lying isomer. We found that the C 2V isomer gains stability from P 5to Sb 5-, consistent with the experimental observation of the coexistence of both isomers in the spectra of Sb 5-. The valence molecular orbitals (MOs) of the D 5h Pn 5were analyzed and compared to those of the aromatic C 5 H 5hydrocarbon. The same set of π-MOs is shown to be occupied in the D 5h Pn 5and C 5 H 5species, except that the MO ordering is slightly different. Whereas the three π-MOs in C 5 H 5all lie above the σ-MOs, the third π orbital (1a 2 ′′ in Pn 5-) lies below the σ-MOs. The stabilization of the π-MO relative to the σ-MOs seems to be common in inorganic aromatic molecules and distinguishes them from the organic analogues.
Cheminform, 2010
The electronic structure and chemical bonding of the pentapnictogen cluster anions, Pn 5 -(Pn ) P, As, Sb, and Bi), were investigated using both photoelectron spectroscopy and ab initio calculations. Well-resolved photoelectron spectra were obtained for the anions at several photon energies and were analyzed according to the theoretical calculations. The ground state of all the Pn 5species was found to be the aromatic cyclic D 5h structure with a C 2V low-lying isomer. We found that the C 2V isomer gains stability from P 5to Sb 5 -, consistent with the experimental observation of the coexistence of both isomers in the spectra of Sb 5 -. The valence molecular orbitals (MOs) of the D 5h Pn 5were analyzed and compared to those of the aromatic C 5 H 5hydrocarbon. The same set of π-MOs is shown to be occupied in the D 5h Pn 5and C 5 H 5species, except that the MO ordering is slightly different. Whereas the three π-MOs in C 5 H 5all lie above the σ-MOs, the third π orbital (1a 2 ′′ in Pn 5 -) lies below the σ-MOs. The stabilization of the π-MO relative to the σ-MOs seems to be common in inorganic aromatic molecules and distinguishes them from the organic analogues.
Journal of the American Chemical Society, 2002
Treatment of a solution of 3-bromo-1-methyl-1,2-dihydroquinoline (9) and [18]crown-6 in furan or styrene with KOtBu followed by hydrolysis afforded a mixture of 1-methyl-1,2-dihydroquinoline (10) and 1-methyl-2-quinolone (11). If the reaction was performed in [D 8 ]THF and the mixture was immediately analysed by NMR spectroscopy, 2-tert-butoxy-1-methyl-1,2-dihydroquinoline (17) was shown to be the precursor of 10 and 11. The structure of 17 is evidence for the title cycloallene 7, which arises from 9 by b elimination of hydrogen bromide and is trapped by KOtBu to give 17 so fast that cycloadditions of 7 with furan or styrene cannot compete. Since this reactivity is unusual compared to the large majority of the known six-membered cyclic allenes, we performed quantum-chemical calculations on 8, which is the parent compound of 7, and the corresponding isopyridine 6 to assess the electronic nature of these species. The ground state of 6 was no longer an allene (6 a) but the zwitterion 6 b. In the case of 8, the allene structure 8 a is more stable than the zwitterionic form 8 b by only % 1 kcal mol À1. These results suggest a high reactivity of 6 and 8 towards nucleophiles and explains the behaviour of 7. In addition to the ground states, the low-lying excited states of 6 and 8 were considered, which are represented by the diradicals 6 c and 8 c and, as singlets, lie above 6 b and 8 a by 19.1 ± 24.8 and 14.4 ± 17.7 kcal mol À1 , respectively.
Journal of the American Chemical Society, 2002
The six-membered cyclic allenes given in the title have been studied theoretically by means of an MR-CI approach. For all compounds, the allene structures were found to be the ground states in the gas phase. In the cases of cyclohexa-1,2-diene (1), the isobenzene 2, and the isonaphthalene 7, the most stable structures having a planar allene moiety are the diradicals 1b, 2b, and 7b, representing the transition states for the racemization of 1a, 2a, and 7a and being less stable than the latter by 14.1, 8.9, and 11.2 kcal/mol, respectively. At variance with this order, the 3delta(2)-pyran 4 and the chromene 5 have the zwitterions 4c and 5c as the most stable planar structures, which lie only 1.0 and 5.4 kcal/mol above 4a and 5a, respectively. According to the simulation of the solvent effect, 4c even becomes the ground state of 4 in THF solution. The frontier orbitals of the respective states of 2 and 4 suggest different rates and sites for the reaction with nucleophiles. For the first time, the pyran 4 has been generated and trapped. As a precursor for 4, 3-bromo-4H-pyran (9) was chosen, the synthesis of which was achieved on two routes from 4H-pyran. The treatment of 9 with potassium tert-butoxide (KOt-Bu)/18-crown-6 gave 4-tert-butoxy-4H-pyran as the only discernible product, whether styrene or furan was present, indicating the interception of 4 by KOt-Bu. Finally, the disagreement between the experiment and the theory concerning the heat of formation and the electronic nature of the isobenzene 2 is resolved by demonstrating that the experimental data can provide only an upper limit of the DeltaH(f) degrees value.
Journal of The American Chemical Society, 1994
A previously reported compound [ N B h ] [ P~~(~-C~F S C~) (~-C~F~) ( C~F S )~] (A) reacts with OHor OR-(R = Me, Et) to give the dinuclear Pt(II1) complexes [NBu~]~[P~~O~-C~F~O)~(C~FS)~] (1) or [NBU~I~[P~~(~-C~F~(OR)~J~-(C6Fs)J with R = Me (2) or Et (3). These three products contain pairs ofquinone ( C6F40) or quinon-like (c6F4(oR)2) bridges and 1 and 2 have Pt-Pt single bonds with lengths of 2.570(1) and 2.584(1) A, respectively. The anions are strictly centrosymmetric and the central C2Pt(p-C)2PtC2 cores have effective mmm symmetry. The p-C6F4(OR)2 ligands are readily hydrolyzed to give p-CsF40 ligands. The crystallographic data are as follows. For 1, Pi, a = 12.055(2) A, b = 12.915(2) A, c = 13.055(2) A, a! = 98.12(1)', 0 = 114.30(1)', 7 = 86.02(1)', V = 1833.7(5) A', 2 = 1. For 2, P21/c, a = 12.220(1) A, b = 21.552(2) A, c = 16.272(2) A, @ = 96.66(1)', V = 4256(1) A3, Z = 2.
Computational Assessment of an Elusive Aromatic N3P3 Molecule
ACS Omega
We computationally proved that the planar aromatic hexagonal isomer N 3 P 3 with the alteration of N and P is the second most stable structure for the N 3 P 3 stoichiometry. We found that the aromatic isomer has high barriers for transition into the global minimum structure or into the three isolated NP molecules, making this structure kinetically stable. We showed that the sandwich N 3 P 3 CrN 3 P 3 molecule corresponds to a minimum on the potential energy surface; thus, the aromatic N 3 P 3 molecule has a potential to be a new ligand in chemistry.
NMR spectra, GIAO and charge density calculations of five-membered aromatic heterocycles
Magnetic Resonance in Chemistry, 2007
The B3LYP/6-31+G(d) molecular geometry optimized structures of 17 five-membered heterocycles were employed together with the gauge including atomic orbitals (GIAO) density functional theory (DFT) method at the B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p) and B3LYP/6-311+G(2d,p) levels of theory for the calculation of proton and carbon chemicals shifts and coupling constants. The method of geometry optimization for pyrrole (1), N-methylpyrrole (2) and thiophene (7) using the larger 6-311++G(d,p) basis sets at the B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p), B3LYP/6-31+G(2d,p) and B3LYP/cc-pVTZ levels of theory gave little difference between calculated and experimental values of coupling constants. In general, the 1 H and 13 C chemical shifts for all compounds are in good agreement with theoretical calculations using the smaller 6-31 basis set. The values of n J HH (n = 3, 4, 5) and rmn J CH (n = 1, 2, 3, 4) were predicted well using the larger 6-31+G(d,p) and 6-311++G(d,p) basis sets and at the B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p), B3LYP/6-31+G(2d,2p) levels of theory. The computed atomic charges [Mülliken; Natural Bond Orbital Analysis (NBO); Merz-Kollman (MK); CHELP and CHELPG] for the B3LYP/6-311++G(d,p) geometry optimized structures of 1-17 were used to explore correlations with the experimental proton and carbon chemical shifts.
Inorganic Chemistry, 2009
As÷MF 3 molecules, which are trapped in an argon matrix. Products are identified from infrared spectra and comparison to theoretically predicted vibrations. Density functional theory calculations converge to C 3v symmetry structures for these lowest energy products. The two unpaired electrons in nitrogen 2p, phosphorus 3p, or arsenic 4p orbitals are shared in different small amounts with empty metal nd orbitals leading to very weak degenerate πR molecular orbitals based on bonding orbital analysis and spin density calculations. This weak π bonding interaction with early transition metal group 4 nd orbitals is optimum for Zr with phosphorus 3p orbitals.
Five and nine membered (heteronines) heterocyclic molecules. Theoretical approach
Tetrahedron, 2001
ÐThe presence or absence of aromaticity in nine membered heterocyclic molecules (heteronines) has been studied from a theoretical point of view (B3LYP/6-311G(2d,p) level). For comparison, the aromaticity of pyrrole, thiophene and furan was analysed. The aromaticity of azonine and thionine is well established along with the problems that arise from the stabilisation of the latter. The origin of oxonine non-aromaticity is discussed in terms of atomic charges and electronegativity. Results for the ion cyclononatetraenide are also reported. Reaction coordinates leading to thionine derivatives are studied. Condensed Fukui functions derived from electronic structure calculations were computed for ®ve and nine membered heterocyclic molecules. These reactivity indices explain the observed products with electrophiles. The stability and the reactivity of these molecules may be understood in terms of the present results.